1. Field of the Invention
The invention relates to a process for testing fluophors and a device for carrying out the process. The invention relates especially to a process for testing fluophors which can be used for testing a substrate for image display, such as a PDP (plasma display panel), FED (field emission display) or the like, and a device for carrying out the process.
2. Description of the Prior Art
A red (R) fluophor, a green (G) fluophor and a blue (B) fluophor (hereinafter called only xe2x80x9cRxe2x80x9d, xe2x80x9cGxe2x80x9d, and xe2x80x9cBxe2x80x9d) are applied to the above-described substrate for image display, such as PDP, FED or the like. By irradiation of the substrate with UV light or the like and by emission of these fluophors a color image is displayed.
If the above-described fluophors have faults or nonuniformities or when the above-described fluophors are mixed with fluophors with other colors, the expected characteristic cannot be obtained. In the production of the above-described substrate for image display, therefore, the state in which the above-described fluophors are applied is checked.
For example, testing of fluophors which are applied to a PDP are described below.
FIGS. 12(a) and 12(b) are each a schematic cross section of a PDP. A PDP has the arrangement shown in FIG. 12(a) in which on a rear substrate 101 (glass substrate: opaque) there are ribs 101a and in which thus pixels (cells) 102 are formed which are covered with transparent glass 103. Fluophors R, G and B are applied to the bottom (side of the rear substrate) and the sides (sides of the ribs) on the inside of the respective cell. Each cell 102 is filled with xenon gas. Above and below the cell one electrode 104a and an electrode 104b, respectively, are formed. By a discharge between these electrodes the xenon gas emits vacuum UV light (147 nm). The fluophors emit fluorescent radiation with the respective color, the emission of this xenon gas acting as the excitation radiation.
In the manufacturing process for PDP, after applying the fluophors R, G, and B to the respective cell on the substrate and before installation of the upper glass 103 in the manner shown in FIG. 12(b), it is checked whether the fluophors have been correctly applied to the respective pixel of the rear substrate 101.
The test has the checks for the following criteria: (1) Whether application to the required locations has taken place; (2) Whether there is any outswelling or fault; (3) Whether R, G, and B are not mixed on the boundary lines; and (3) Whether there is any nonuniformity of application, as shown, for example, in FIG. 13. Occasionally the following test criteria is herein generally referred to as xe2x80x9ctesting of the application state.xe2x80x9d
In order to test the state of application of the fluophors, the fluophors must be caused to emit. The reason for this is that the above-described fluophors which emit R, G, and B are white under visible radiation and that they cannot be distinguished from one another.
To cause the fluophors to emit, the fluophors are irradiated with excitation light. Conventionally, the light source of this excitation light is a super-high pressure mercury lamp or a xenon lamp. For the light from these lamps, however, the fluophors G and B emit fluorescent light in a sufficient amount, but the fluophor R hardly emits. Therefore, only an emission intensity of roughly {fraction (1/10)} to {fraction (1/50)} of the fluophors G and B was obtained. Therefore, mixing of R with other colors and outswelling could not be easily differentiated and the time consumption for the test was very high.
Further, since the amount of light of R is smaller than G or B there are cases in which the emission limit of the measurement device is not reached; this prevents automation of the test. For a xenon lamp, xenon gas is discharged and thus emission is carried out. But since the glass comprising the arc tube of the lamp does not transmit light with a wavelength of 147 nm, fluophors cannot be irradiated with light with a wavelength of 147 nm using a xenon lamp.
The emission of R is dark because the energy required for excitation of the fluophor R is greater than the energy required for excitation of the fluophor B or G. With the light from the above-described super-high pressure mercury lamp or from the xenon lamp, therefore, the fluophor B and G can be excited, but the fluophor R cannot be excited to a sufficient degree.
The fluophor R is often, for example, an oxide based on mixed elements of rare earth metals which is described by the general formula (Y1-a-bGdaEub)2O3 (however, 0 less than axe2x89xa60.90, 0.01xe2x89xa6bxe2x89xa60.20) or a boron oxide based on mixed elements of the rare earth metals is used which is described by the general formula (Y, Gd, Eu)BO3 or (Y, Gd)BO3.
With respect to the excitation energy however, in any case, the situation is the same. Sufficient fluorescence cannot be obtained by the light from a super-high pressure mercury lamp or a xenon lamp.
The invention eliminates the above-described disadvantages in the prior art. The object of the invention is to enable the application state of the fluophors to be easily tested within a short time while, at the same time, enabling the application state of the fluophors to be automatically tested, by increasing the emission amount of red (R) such that it is made the same as the emission amount of green (G) and blue (B). A light with a shorter wavelength than the wavelengths of the light emitted from a super-high pressure mercury lamp or a xenon lamp is used as excitation light for sufficient excitation of the fluophor R light. When the wavelength becomes shorter, the photon energy becomes accordingly greater.
As a result of various studies, it was found that when a light source is used which emits light with a wavelength less than or equal to 230 nm, the emission amount of the fluophor R can be increased and it can then make the amounts of emission of the fluophors G and B the same. In the case of a wavelength of less than or equal to 200 nm, however, a large amount of ozone is formed. Therefore, it is difficult to use it in air and its use as a light source of a test device is not possible.
Therefore, it is desirable in testing of fluophors to use a lamp which can emit light with wavelengths from 200 to 230 nm with sufficient radiation intensity.
These lamps were studied and it was found that (1) Discharge lamp of the short-arc type in which an arc tube is filled at least with cadmium and rare gas and which has emission lines between 200 nm and 230 nm; and (2) Dielectric barrier discharge excimer lamp which has electrodes for carrying out a dielectric barrier discharge and a discharge vessel which is filled with krypton gas and chlorine gas, in which light emerges which is emitted by krypton chloride excimer molecules which have been produced by this dielectric barrier discharge, and which has emission lines between 200 nm and 230 nm.
A type (1) discharge lamp of the short-arc type is described, for example, in the Japanese patent specification 2775694 described below (JP-OS HEI 6-318449 corresponding to U.S. Pat. No. 5,481,159) and in the Japanese patent specification 3020397 described below (JP-OS HEI 7-21980 corresponding to U.S. Pat. No. 5,471,278) and the like. Such a lamp has emission spectra at a wavelength in the vicinity of 215 nm; and
A type (2) dielectric barrier discharge excimer lamp is described, for example, in the Japanese patent specification 3171004 described below and the like. One such lamp has emission spectra at a wavelength in the vicinity of 222 nm. Furthermore, a dielectric barrier discharge excimer lamp is known which emits light with a wavelength of at most 200 nm. When such a lamp is used, as was described above, a large amount of ozone is formed. Therefore, such a lamp cannot be used for a test device in practice.
If, using the above-described lamps as the excitation light source, the above-described fluophors are illuminated, the fluophor R also emits with the same amount of light as G and B. In this way, it is possible to carry out the test easily, and moreover, in a short time.
Furthermore, using the above-described lamps, a test device for fluophors can be arranged in the manner described below.
The above-described type (1) or (2) lamps are used for the light source. The fluophors are irradiated with light from this light source, the fluorescence emitted from these fluophors is received by a CCD sensor or the like, it is displayed in a display device or the like and the application state, such as faults or the like of the fluophors, is checked. Furthermore, the images detected by the CCD sensor can be input to a control device and testing can be automated.
An above-described type (2) lamp that is rod-shaped is used for the light source. The light emitted from this lamp is focused by means of a trough-like focusing mirror, the fluophors are irradiated with it and the light produced by the fluophors is received by the CCD sensor. The fluophor application surfaces as test articles or the above-described dielectric barrier discharge excimer lamp are moved relative to the CCD sensor such that all fluophor application surfaces are irradiated with the light from the above-described lamp. The images received by the CCD sensor are displayed in the display device or the like and the application state, such as faults or the like of the fluophors, is tested. Furthermore, the images picked up by the CCD sensor can be input into a control device and testing can be automated.
The above-described discharge lamp of the short arc type is used for the light source. The light emitted by this lamp is focused by means of a focusing mirror, is routed through optical fibers onto the fluophor application surfaces, the fluophors are irradiated with it and the light produced by the fluophors is received by the CCD sensor. The fluophor application surfaces as the test items or the optical fibers and the CCD sensor are moved relative to one another such that all fluophor application surfaces are irradiated with light from the above-described lamp. The images picked up by the CCD sensor are displayed in the display device or the like and the application state, such as faults or the like of the fluophors, is checked. Furthermore, the images picked up by the CCD sensor can be input to a control device and testing can be automated.
By the above-described measure that the fluophor application surfaces as the test articles or the above-described lamp or the optical fibers and the CCD sensor are moved relative to one another such that all fluophor application surfaces are irradiated with light from the lamp, the test articles can be checked within a short time. In particular, by using a rod-shaped dielectric barrier discharge excimer lamp all fluophor application surfaces can be irradiated with light from the lamp by only one-time scanning and testing can be done within a short time. Furthermore, by automating the test the test duration can be shortened even more than in a visual check.